The present disclosure generally relates to resin blends and articles comprising thermoplastic polymers derived from 2-hydrocarbyl-3,3-bis(4-hydroxyaryl)phthalimidine monomers. More particularly, the present disclosure relates to resin blends and articles comprising a polycarbonate comprising structural units derived from phenolphthalein derivatives, such as 2-hydrocarbyl-3,3-bis(4-hydroxyaryl)phthalimidine monomer and an ABS (acrylonitrile-butadiene-styrene) resin. Still more particularly, the present disclosure relates to resin blends and articles comprising a polycarbonate comprising structural units derived from relatively pure 2-hydrocarbyl-3,3-bis(4-hydroxyaryl)phthalimidine.
It is well known that plastic substrates are rendered fire-retardant by the use of fire-retardant additives. Polymer blends comprising an ABS resin, such as for example, a polycarbonate-ABS blend are particularly challenging substrates due to the inherently high flammability of the ABS resin component. Blends of polycarbonates with styrenic polymers, such as the ABS resins mentioned above are typically rendered fire-retardant by the addition of organic phosphorus compounds, such as resorcinol 1,3-diphenylphosphate (abbreviated as “RDP” throughout this disclosure) and bisphenol A bis(diphenyl)phosphate (abbreviated as “BPADP”), which are generally believed to act in a vapor phase by quenching free radicals that can be responsible for the propagation of the fire. It is also known that an effective amount of the organic phosphorus compound necessary for achieving a given degree of fire retardance can be reduced by employing appropriate synergists, such as siloxanes, inorganic fillers, etc.
Further, for resin blends comprising highly flammable polymers, such as the ABS resins, it is necessary to add relatively large amounts, sometimes as high as the amount of the ABS resin present in the resin blend to achieve robust flame performance (such as for example, the Underwriter Laboratories' rating of “V0” as defined in a UL94 standard) for molded parts having relatively thin walls (example, less than or equal to 2 millimeters wall thickness. However, the addition of relatively high amounts of the fire-retardant additives based on organic phosphorus compounds can lead to number of disadvantages in the final blend, such as for example, inferior heat characteristics (heat distortion temperature) due to the plasticizing effect of the organic phosphorus compounds; poor mechanical properties, such as room temperature impact and tensile modulus, among others. Also, these additives are known to bloom to the surface during aging, thereby resulting in poor aesthetics. Further, there are environmental health and safety concerns during operations, such as for example, during processing, incineration, or recycling of plastic materials containing organic phosphorus-based compounds as fire-retardants. These concerns have prompted the industry to seek alternative, “greener”, or more environmentally friendly fire-retardants. Due to the wide applications of fire-retardant plastics for modern day living, a safer and more environmentally friendly non-phosphorus fire-retardant additive would be greatly beneficial to the plastics manufacturing and processing industries. In particular, such a fire-retardant additive will be able to enhance the utility (for example, in the consumer products industry) of polymer blends based on ABS resins, such as for example, the polycarbonate-ABS blend.
Therefore, there is a need for fire-retardant polymer blends containing effective fire-retardant additives that not only are phosphorus-free, but also do not affect the desired physical properties of the blends, such as for example, impact, tensile modulus, and the like. Further, there is a need for polymeric fire-retardant additives that can help retain the properties of the polymer blend, as compared to the low molecular weight fire-retardant additives, such as RDP and BPADP, which act as plasticizers, as described previously.
Phenolphthalein has been used as an aromatic dihydroxy compound monomer for preparing polycarbonates, which are generally characterized with excellent ductility and high glass transition temperatures. Certain derivatives of phenolphthalein have also been used as aromatic dihydroxy compound monomers to prepare polycarbonate resins as well as polyarylate resins. For example, polycarbonate homopolymers have been prepared by an interfacial polycondensation method using phosgene and monomers such as 3,3-bis(4-hydroxyphenyl)phthalimidine and 2-phenyl-3,3-bis(4-hydroxyphenyl)phthalimidine (hereinafter sometimes referred to as “para,para-PPPBP”).
Lin and Pearce (Journal of Polymer Science: Polymer Chemistry Edition, (1981) Vol. 19, pp. 2659-2670) reported the synthesis of para, para-PPPBP for preparing polycarbonates and other polymers by refluxing phenolphthalein and aniline hydrochloride in aniline for 6 hours, followed by recrystallization from ethanol. During this reaction, side products are created which, if not removed, can result in para, para-PPPBP having an unacceptable purity for use as a monomer or as a comonomer. The undesirable side products or impurities generally include both inorganic and organic species. With regard to the manufacture of polycarbonate, the impurities can hinder polymerization and result in low weight average molecular weight polycarbonates, example, less than about 22,000 Daltons for melt polymerization and less than about 50,000 Daltons for an interfacial polymerization that exhibit undesirable physical properties, such as increased brittleness, that is, poor ductility properties. Furthermore, the impurities in the para, para-PPPBP monomer include, for example, trace (parts per million) levels of phenolphthalein or phenolphthalein residues that can undesirably produce discoloration in the polycarbonates and other polymers derived therefrom, thereby affecting the transparency of the polymer product. Coloration is not desirable for many commercial applications. U.S. Pat. No. 5,344,910 discloses that copolymers of para, para-PPPBP were found to have poor melt stability resulting in foamy polymer melts and moldings, and discoloration of the resin during melt processing.
It would therefore be desirable to develop a process for preparing relatively pure phenolphthalein derivatives such as 2-hydrocarbyl-3,3-bis(4-hydroxyaryl)phthalimidine, which can then be used for producing polycarbonates and other polymers having improved properties, such as lower color, e.g., a low yellowness index (YI) of less than about 10, and higher weight average molecular weight. Further still, there is a need for such resin blends and articles having excellent fire retardance and improved physical properties.